Researchers in the United States have developed a method that helped them observe the sunlight-to-fuel conversion in real time, right down to the nanoscale.
The team of Yale researchers can now see how the light-driven catalyst splits water into hydrogen and oxygen, and how electrons and holes move through the material.
“We are excited because this method lets us see a photocatalyst ‘in action’ with an unusual combination of realism and resolution,” said Shu Hu, professor of chemical & environmental engineering, who led the study.
New way to watch photocatalysts work in real time
Researchers revealed that their study introduces a new way to watch photocatalysts work in real time and at extremely small scales of about 10 nanometers.
This overcomes a key limitation in the field, and could help improve technologies that use sunlight to produce clean fuels and chemicals. The work reveals the precise division between two chemical reactions — reduction and oxidation. This insight could pave the way for designing better solar-fuel materials, according to a press release.
The research team created a system that simultaneously makes amperometric and potentiometric measurements. Amperometric measurements account for the number of electrons that flow. Potentiometric measurements determine the voltage, or force that propels the electrons. To do so, they created a “nanotip,” a very fragile nanoscale quartz tip with a nanometer-sized platinum wire in the center.
One challenge of their work was bringing the nanotip into physical contact with the surface without damaging it and maintaining very precise positional control.
A major surprise of their work was that they could measure the electrical current of not only the metallic surfaces, but also the voltage of the semiconductor materials while under light, according to Hu.
The work introduces a unique approach based on a single setup employing contact amperometric/potentiometric photo-scanning electrochemical microscopy for quantitative, high-resolution measurements of photoelectrochemical processes in nanostructured photocatalysts.
Cost-efficient energy and chemical production
Researchers revealed that solar-power photocatalysis – turning sunlight into energy – holds promise for sustainable and cost-efficient energy and chemical production. Advancing the technology, though, has been hindered by a lack of understanding of exactly how the process works.
Researchers revealed that this methodology resolves spatial variations in photocatalytic reactivity of nanoscale cocatalysts supported on semiconductors with a spatial resolution on the order of 10 nm.
“In the Pt/Nb:TiO2 system, this method identifies distinct cathodic and anodic sites separated by ~150 nm, with local surface potentials of approximately −0.53 V and +0.58 V vs. Ag/AgCl, respectively,” said researchers in the study.
“Complementary structural/compositional and spectroscopic analyses reveal the coexistence of metallic Pt and oxidized Pt species under OWS conditions, establishing asymmetric surface energetics consistent with a ~1.5 eV difference in local band-edge position and thereby driving directional carrier separation within Nb:TiO2,” added researchers.
The study was published in Proceedings of the National Academy of Sciences.